The present invention relates to a buckle pretensioner for a vehicle safety restraint.
Pretensioners are used to rapidly withdraw a length of seat belt webbing in the event of an emergency. This takes up slack in the seat belt which might be caused by bulky clothing or by a vehicle occupant being out of position such as when leaning forward in the seat, or when seated skewed for example when asleep. The purpose of eliminating this slack is to more securely restrain the vehicle occupant at the onset of emergency conditions, and to more correctly position him for maximum effect of any secondary safety restraint such as an airbag.
Pretensioners may be situated at the retractor end of a three-point safety belt to rapidly rewind the belt webbing, or alternatively at the buckle end to rapidly pull back the buckle mounting.
Known buckle pretensioners use a piston-cylinder arrangement in which a piston connected to the buckle mounting is pushed rapidly along a cylinder by the force of a spring or more recently by pyrotechnic means which release a sudden rush of gas. Such arrangements are bulky and difficult to fit unobtrusively in a vehicle, particularly in the smaller models of vehicle which are popular nowadays.
It is an object of the present invention to provide an improved buckle pretensioner and particularly a more compact design.
According to the present invention there is provided a buckle pretensioner for a vehicle safety restraint comprising a buckle head for receiving a buckle tongue to secure safety restraint webbing about a vehicle occupant in a three-point belt system, the pretensioner comprising; a cable connected to the buckle head and means for rapidly withdrawing the cable in a belt tightening direction, the withdrawing means comprising a force generator or reservoir and driving means and being more compact than hitherto known.
According to a first embodiment of the invention the pretensioner further comprises step-up gearing means for converting a linear movement of a predetermined magnitude, produced by the force generator, into a linear movement of the cable of more than the predetermined magnitude, preferably a multiple of the predetermined magnitude.
Gearing arrangements were not previously considered viable for pretensioners, particularly buckle mounted pretensioners because they increase the torque which must be generated by the driving means, the maximum torque from traditional driving means was limited. However the improvements in pyrotechnic force generators means that sufficient torque can now be generated rapidly enough.
The step-up gearing may comprise a multiple pulley arrangement, such that the withdrawal means operates on a small diameter pulley fixedly connected to rotate with a large diameter pulley about which the cable is wound.
This arrangement allows a relatively simple force reservoir to be used in the pretensioner because the necessary locking devices can be included in the pulley arrangement, for example a simple ratchet and stop, rather than being part of the force generator (for example in the tube of a piston-cylinder pretensioner) as hitherto.
This embodiment can also be adapted relatively easily to incorporate load limiting features.
It is particularly applicable to the use of a piston-cylinder type pretensioner, either with a spring or a pyrotechnic force generator and the cylinder tube can in this case be made much shorter than in previous pretensioners.
However this embodiment is equally applicable to other types of force generator or to other driving means.
According to a second embodiment the driving means comprises a rack and pinion arrangement. The rack may be vertical or horizontal and is driven past the pinion wheel which is connected to rotate a pulley about which the cable is wound, by spring force or by a gas generator.
The pinion wheel may be driven by more than one rack, as for example in a system with two moving racks one on either side of the pinion wheel in opposite directions to reinforce each other""s driving force. Their movement may be synchronised or phased depending on the pretensioning characteristics to be achieved.
Force generators such as gas generator may be integral with the racks.
Gearing arrangements may advantageously also be incorporated in this embodiment.
According to a third embodiment, the driving means comprises at least two pulley wheels across which the cable passes and means for extending the distance between the pulley wheels so as to withdraw the cable in the belt tightening direction.
Two pulley wheels may be arranged adjacent the path of the cable and driven in opposite directions across the path of the cable so as to withdraw the buckle head.
Alternatively two or preferably more pulley wheels are arranged with the buckle cable wound around them in an S configuration and one or more pulley wheels are driven parallel to the cable to withdraw the buckle head.
A further alternative is to use an elongate, elliptical or oval, cam pulley, arranged in normal use with the cable passing along both its long sides and round one of its short sides. Under pretensioning conditions this cam pulley is rotated rapidly through approximately 90xc2x0 so that its long sides are tangential to the path of the cable from the buckle head, thus quickly and easily shortening the effective length of cable from the buckle head to its mounting position. The cam pulley may be driven by a pyrotechnically detonated gas generator or by a spring, or by other force generator means.
A gas generator driven cam faced piston may be used instead. The buckle cable passes over the outer arcuate cam face of the piston. When pretensioning is required the gas generator drives the piston a predetermined distance away from the buckle head and thus shortens the effective length of the cable to the buckle head.
According to a fourth embodiment of the invention the driving means comprises a rotating part with paddles or vanes driven by gas from a gas generator. This may be a wheel connected to the cable pulley, with or without gearing, or a helix coaxial with the cable pulley.
Alternatively a Roots motor or gear pump could be used comprising two camming figure-of-8 drive parts, one driven by a gas generator, the other coaxial with the cable pulley.
For a better understanding of the present invention and to show how the same may be carried into effect, reference will now be made to the accompanying drawings, in which: